Heretofore multi-finger rotary drill bits have a life span limited mostly by bending and breaking of the relatively long straight narrow fingers due to abrading away of the relative small amount of initial outer surface area and resulting reduced cross sectional area thereof.
Also, the initial small amount of surface area and the narrow straight projecting fingers provided very limited bit stabilization in the hole. Thus, the insufficiently stabilized bit vibrates and moves laterally in the hole causing the bit to deviate and the hard surfaces of the cutting element to flake away as they sharply strike the hard earth formations.
Multi-finger drill bits inherently cut a central core and when hard formations are encountered the cutting or penetration rate is greatly reduced or stopped if they are unable to rapidly grind, cut or break up and eject the core material.
Many prior art drill bits depend solely on the composition and an internal inclined surface of the bit blank or body to engage and break off the core produced. Others are known to have a non-cutting wear resistant core breaker insert with an inclined surface to prevent abrading of the body.
Also known are a number of composite spiral or helically fluted drill bits tipped or provided with hard cutting inserts of harder wear resistant material than the supporting body. Various cutting inserts have been made comprising various metal carbides, borides, nitrides, oxides, cubic boron nitride, natural and synthetic diamonds and mixtures or alloys thereof.
There are commercially available both diamond and boron nitride abrasive composite compact cutting inserts made and sold by General Electric under their registered tradenames "Stratapax" and "Compax" utilized in the manufacture of various types of oil drilling bits.
The Applicants' drill bit differs from those of the prior art in that it has a machined or investment cast body including shorter, stronger helically or spirally curved fingers of greater cross sectional area backed by reinforcing webs supporting composite compact cutting inserts, wide overlapping helical or spiraly stabilizing lands extending from the fingers substantially the entire length of the bit, helical or spiral grooves between the lands for rapidly conveying and flushing cuttings upwardly from the hole and a hard core cutter-breaker insert including an inclined cutting edge to rapidly cut away and break up relatively hard core formations.